Cream cheese and jelly sandwich weirdness

A little background first. My a1c is 5.7, my fasting glucose is always in the 100-115 range, pre-meal norm is 100-110. 2 hours post meal I'm usually back into the 120s. This is just the reality of my body.

Lately I've been having the occasional cream cheese and jelly sandwich at lunchtime. I use 2 slices of Dave's killer whole grain bread, 1oz of Philadelphia cream cheese (full fat), and 2-3 tablespoons of Welch's grape jelly. Dinner is usually around 5:30, lunch around noon. At dinner I'm usually in the 100-110 range, but I have noticed that after eating my sandwich, which is 70g carb, I'll be in the high 90s by dinner time and starting to crash every time. Tonight I tested at 5:09pm and was at 98 and I knew I was going down, I could feel it. At dinner time 6pm, I was at 70 and definitely crashing. I even had a piece of fruit cake around 3pm because I knew I'd be low by dinner.

I'd love to hear if anyone has any insights on why I crash after 4 hours when I eat this sandwich. If I had eaten almost anything else at 70g carb, I would probably still be up above 130 at 6pm.